I just got a griffin radiator for my 66 from summit racing. 189.99 and it was here in four days. I put it in this last weekend and I haven't seen it run past 180 at all. I used to run 200-210 on 50 degree days.
If you don't mind making some modifications and aren't going for a stock look I would stongly suggest you get one. I don't remember what the part number is but if you just look for the 19 x 31 inch dual core radiator you will probably find it. Or if you want to drop the cash BeCool sells a radiator for 71-80 Camero and Firebirds that is supposed to work with 65 and 66 big pontiacs, but for 500.00, Ouch. It would probably fit without making any modifications. I'm just cheap, and I figured I could get the same thing for less if I just put a little work into making it fit. Plus I'm so far from stock with my car that the "numbers matching" people would probably burn me at the stake.